National Center for Immunization and Respiratory Diseases

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The disease often begins with symptoms that can be easily mistaken for such common illnesses as the flu or a cold, noted Stacey W. Martin, an epidemiologist with the CDCâ€™s National Center for Immunization and Respiratory Disease.
Symptoms generally appear six to 21 days after exposure to an infected person.

â€œLot of the infected people who are walking around are adults, and many of them donâ€™t know they are carrying it,â€ Heyes said.

Around 75 to 85 percent of the disease is transmitted in households, Martin said, which is why it is important that every family member gets vaccinated.

"We rushed to do this study in Vermont after we saw this change," CDC epidemiologist Stacey Martin said.
In 2010, less than 10 percent of whooping cough cases in the U.S. involved the new strain, while in 2013, more than 90 percent of the cases were from the new strain.
"To have that happen so quickly across the entire U.S. is something that we needed to better understand," Martin said.

There have been more than 16,000 cases of whooping cough in the U.S. so far this year, said Stacey Martin, an epidemiologist with the Centers for Disease Control and Prevention (CDC).
Latest projections indicate that this will be a record year, she said.

The previous record was 27,550 cases in 2010, when it killed 27 people, including 25 babies.

There are several factors that contribute to this problem.
Infants younger than two months are too young to be vaccinated, making them vulnerable.
Also, the formulation for the vaccine was modified in the 1990s for safety reasons, rendering them less effective, Martin said.

Stacey Martin, a CDC epidemiologist, said the cycles typically last two to five years at a time, but that the intervals between the outbreaks appear to be shrinking.
Part of the explanation is the change in the type of vaccine given to children in the 1990s, which has a shorter period of effectiveness.

Martin said that vaccine has fewer adverse side effects and reactions than the older one, but the downside is that it may not last as long.
Some of the new cases are in children who are at or approaching adolescence, she said.

"It emphasizes the need for the booster for 11 to 12 year olds," she said.